The present invention relates to (1) a compound having a six-membered ring lactone and a norbornane ring in the same molecule and its monomer, (2) a high-molecular compound containing the monomer as a constituent unit, (3) a resist material containing this high-molecular compound, and (4) a pattern forming method using this resist material.
In recent years, as operation data to deal with and the amount of processing two-dimensional and three-dimensional image data have become enormous by the development of computers and digital equipment represented by electric home appliances, high-capacity and high-speed semiconductor devices are necessary. Along with the development of network such as Internet, the processing capacity required for digital equipment is becoming higher.
In order to achieve this requirement, higher density and higher integration of semiconductor devices, that is, finer pattern rule is required. As one of means for achieving finer ones, it is known to shorten the wavelength of an exposure light source used when resist pattern is formed. Hitherto, i-line (365 nm) of high-pressure mercury light and KrF excimer laser light (248 nm) have been used as the exposure light source. Now, 0.13 μm or less is required as the minimum line width. Since i-line and KrF excimer laser light used hitherto cannot respond to the processing for that, the use of ArF excimer laser (193 nm) has begun. The development of photolithography technique using F2 (157 nm) and EUV extreme ultraviolet rays is in progress for the purpose of processing finer patterns.
In ArF excimer laser lithography, since resins such as novolac and polyvinylphenols (aromatics) used for KrF excimer laser have a strong absorption at around 193 nm, they cannot be used as base resins for ArF resist. Therefore, acrylic resins, which are replacement of aromatic by aliphatic for improving transparency, are mainly studied. As to F2 laser lithography, finer ones of 0.10 μm or less is expected, and it is found that fluorine-containing polymers are effective for securing transparency.
The base resin is required to have capacities such as acid lability, etching resistance and substrate adhesion as well as transparency to laser light. Since there is no monomer having all the capacities, it is tried to satisfy the required characteristics by using a copolymer formed from a plurality of monomers having respective capacities. However, high molecular compounds capable of practical use have not yet been obtained. Thus, the development of various monomers that sufficiently demonstrate respective capacities is now actively going on.
Above all, the development of a monomer having substrate adhesion has been difficult. This is because, since substrate adhesion has been achieved up to now by hydroxy group and carboxy group, which are hydrophilic groups, and in contrast etching resistance has been provided by polycyclic hydrocarbon groups such as adamantyl and norbornyl, the by-production of homopolymers, the formation of block copolymers and the like have occurred frequently, and therefore it has been difficult to make the reaction proceed homogeneously. It has been found that resist resolution lowers extremely by using a high molecular compound obtained under such condition as a base resin of resist material. That is because there occur swelling caused by penetration of a developing solution into a hydrophilic moiety arranged biasedly, pattern collapse caused by exfoliation of a highly hydrophobic moiety, inhomogeneous dissolution caused by resist film inner layer separation, and the like.
In order to solve the above problems, a tricyclic lactone having a five-membered ring lactone structure and a norbornane ring has recently been developed (see Japanese Patent Laid-open Publication No. 2000-26446 and Japanese Patent Laid-open Publication No. 2000-159758). Since this has in the same molecule a five-membered ring lactone structure as a hydrophilic group for providing substrate adhesion and a norbornane ring as a hydrophobic group, the separation of the hydrophilic moiety and the hydrophobic moiety cannot occur in principle. As a result, it was confirmed that a homogeneous high molecular compound having a good dissolution characteristic is obtained and that stiffness of the condensed tricyclic moiety provides the high molecular compound with a sufficient etching resistance. However, it was found that, since the five-membered ring lactone is stiff beyond expectation, all of the unshared electron pairs of the oxygen atoms of the lactone moiety cannot contribute to substrate adhesion, and it is inferior to the expected capability and is still insufficient for practical level. Furthermore, the polymerization solvent is limited since its dissolution in organic solvent is low. It was very difficult to remove the monomer upon purification of the high molecular compound. Therefore, creation of a novel lactone-containing monomer or its raw material, which can overcome those defects, was strongly desired.